Tray would spin on the surface (9)
I believe the answer is:
outwardly
'on the surface' is the definition.
(I've seen this in another clue)
'tray would spin' is the wordplay.
'spin' indicates anagramming the letters.
'tray'+'would'='traywould'
'traywould' is an anagram of 'OUTWARDLY'.
(Other definitions for outwardly that I've seen before include "Superficially" , "As far as appearances are concerned" , "On the face of it" , "Externally" .)